WASHINGTON (AP) — An unmanned Army surveillance blimp that broke loose from its ground tether at a U.S. military base in Maryland on Wednesday, coming down in Pennsylvania, its tether snapping power lines and causing outages along the way.

The chief spokesman for the North American Aerospace Defense Command says the blimp drifted over Pennsylvania and “grounded itself,” but the military does not know why it deflated as its descended.

An unmanned Army surveillance blimp which broke loose from its ground tether in Maryland floats through the air about 1,000 feet about the ground while dragging a several thousand foot tether line just south of Millville, Pa., Wednesday, Oct. 28, 2015. (Jimmy May/Bloomsburg Press Enterprise via AP) MANDATORY CREDIT

He says it was tethered to a mooring station at an altitude of about 6,600 feet when it broke free about 12:20 p.m. He says it is not known how it detached from its mooring, but an investigation is underway.

Miller says two armed Air Force F-16 fighter jets tracked the runaway blimp as it drifted north from Aberdeen Proving Ground. He says there was never any intention of shooting down the blimp.

Pennsylvania State Police say the blimp came down near Muncy, about 80 miles north of Harrisburg.

Witnesses reported seeing the blimp drifting in area north of Harrisburg, the state capital. Its tether was snapping power lines.

The local electric utility, PPL, reported about 20,000 customers without power in the area, although it was unclear how many could be attributed to the blimp. Bloomsburg University canceled classes, citing a “widespread power outage.”

The blimp is the kind used extensively in the Iraq and Afghanistan wars to provide ground surveillance around U.S. bases and other sensitive sites.

“My understanding is, from having seen these break loose in Afghanistan on a number of occasions, we could get it to descend and then we’ll recover it and put it back up,” Defense Secretary Ash Carter said in a brief exchange with reporters at the Pentagon. “This happens in bad weather.”

Carter did not say what the two F-16 fighters tracking the runaway blimp might be asked to do or whether he considered it a threat to aviation.

The F-16s were launched from the Atlantic City Air National Guard Base in New Jersey, according to the NORAD statement.

U.S. aviation officials were working with the military to ensure air traffic safety in the area.

The aircraft is known as a Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System , or JLENS, and can be used as part of a missile defense system.wb